mvtr

MVTR, or Moisture Vapor Transmission Rate, measures the rate at which water vapor passes through a material. It is commonly expressed as grams of water per square meter of material per day (g/m2/day) under specified temperature and humidity conditions. A higher MVTR indicates greater moisture vapor transmission (a more breathable or less effective moisture barrier), while a lower MVTR indicates a tighter barrier.

MVTR is used in several fields. In textiles and apparel, MVTR relates to fabric breathability and wearer comfort. In packaging, particularly for foods, pharmaceuticals, and electronics, MVTR assesses moisture protection and shelf life. In coatings and membranes, MVTR informs barrier performance.

Measurement: The standard method is ASTM E96, which defines two primary test methods: the desiccant method (E96A) and the water method (E96B). These tests are conducted with a permeation cell or cup, under controlled temperature and humidity, often at 23°C and a specified humidity gradient (for example, 0% vs 50% RH or 50% vs 90% RH). Some industries use ISO, JIS, or other regional standards. The MVTR value depends on thickness, porosity, seals, coatings, and test conditions; thin films generally show higher MVTR than thick or layered structures.

Interpretation: MVTR should be compared only for identical test conditions. It is a measure of steady-state vapor transmission and does not capture all real-world moisture transport, such as during flexing, UV exposure, or long-term aging.